1. Field of the Invention
This invention relates to polyesteramides and is more particularly concerned with blends comprising polyesteramides and minor amounts of urethane group containing ingredients, and, optionally, antioxidants.
2. Description of the Prior Art
Linear polyesteramides belong to a well known class of polymers which are characterized by the presence of recurring amide and ester linkages in the molecule. By joining polyester groups and polyamide groups through various types of linkages, and, particularly in the form of block copolymers, the beneficial physical properties characteristic of polyamides such as tensile strength, impact strength, toughness, etc. can be realized while at the same time enjoying the benefits of an elastomeric material which latter property is not characteristic of polyamides alone. For a representative group of polyesteramides see those disclosed in U.S. Pat. Nos. 3,272,774; 3,468,975; 3,849,514; 4,129,715 and 4,182,842.
In common with many polymers, polyesteramides can lose mechanical properties upon exposure to elevated temperatures for extended periods of time. This loss is reflected particularly in the lowering of tensile properties, i.e., modulus, tensile strength, and elongation properties. These losses can occur either through high temperature processing (e.g. injection molding or extruding) or during some end-use application (e.g. hydraulic lines carrying fluids at high temperatures).
U.S. Pat. No. 3,904,706 discloses stabilized copolyetherester polymers which contain polyalkylene oxide blocks. The ether blocks, and thus the polymer itself, are stabilized by blending into the polymer the combination of a small amount of a urethane containing compound plus an antioxidant. However, the degree to which the physical properties of the stabilized polyetherester elastomers are maintained under elevated temperature is minimal. In fact, such polymers appear to have a very limited high temperature application capability.
We have now discovered that blending minor amounts of urethane ingredients alone with polyesteramide polymers results in the polyesteramides having enhanced thermal stability which is reflected in the polymers retaining their good tensile properties to a substantial degree when subjected to high temperatures.
Surprisingly, this enhancement in thermal properties, particularly with the additional presence of standard types of antioxidants in the blends of this invention, occurs to a greater extent than is the case for the copolyetherester polymers disclosed in U.S. Pat. No. 3,904,706 cited supra.
Additionally, the blends in accordance with the present invention possess other quite unexpected advantageous features compared to the polyesteramide alone which features will be discussed below.
The improved thermostability enables the present polymers to be utilized in high temperature applications not heretofore possible for polyesteramides.